linux-kernel - Re: [PATCH v2] drm: gem_cma_helper.c: Allow importing of contiguous scatterlists with nents

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Date:   Sat, 11 Nov 2017 14:47:35 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Liviu Dudau <Liviu.Dudau@....com>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        Brian Starkey <brian.starkey@....com>,
        Mali DP Maintainers <malidp@...s.arm.com>,
        DRI-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        intel-gfx@...ts.freedesktop.org, Liviu Dudau <liviu.dudau@....com>
Subject: Re: [PATCH v2] drm: gem_cma_helper.c: Allow importing of contiguous scatterlists with nents > 1

Hi Liviu,

Thank you for the patch.

On Friday, 10 November 2017 15:33:10 EET Liviu Dudau wrote:
> drm_gem_cma_prime_import_sg_table() will fail if the number of entries
> in the sg_table > 1. However, you can have a device that uses an IOMMU
> engine and can map a discontiguous buffer with multiple entries that
> have consecutive sg_dma_addresses, effectively making it contiguous.
> Allow for that scenario by testing the entries in the sg_table for
> contiguous coverage.
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Signed-off-by: Liviu Dudau <liviu.dudau@....com>
> ---
> 
> Laurent,
> 
> Thanks for the review! I would like to ask for one more favour: if you
> are OK with this version, can you pull this patch through the drm-misc tree?

I could, but I'd first need to set dim up, and I'm currently abroad with a bad 
internet connection and a big deadline for the middle of next week (I know, 
lots of excuses), so it's not very convenient for me at this time.

>  drivers/gpu/drm/drm_gem_cma_helper.c | 22 ++++++++++++++++++++--
>  include/drm/drm_gem_cma_helper.h     |  4 +++-
>  2 files changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c
> b/drivers/gpu/drm/drm_gem_cma_helper.c index 020e7668dfaba..43b179212052d
> 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -482,8 +482,26 @@ drm_gem_cma_prime_import_sg_table(struct drm_device
> *dev, {
>  	struct drm_gem_cma_object *cma_obj;
> 
> -	if (sgt->nents != 1)
> -		return ERR_PTR(-EINVAL);
> +	if (sgt->nents != 1) {
> +		/* check if the entries in the sg_table are contiguous */
> +		dma_addr_t next_addr = sg_dma_address(sgt->sgl);
> +		struct scatterlist *s;
> +		unsigned int i;
> +
> +		for_each_sg(sgt->sgl, s, sgt->nents, i) {
> +			/*
> +			 * sg_dma_address(s) is only valid for entries
> +			 * that have sg_dma_len(s) != 0
> +			 */
> +			if (!sg_dma_len(s))
> +				continue;
> +
> +			if (sg_dma_address(s) != next_addr)
> +				return ERR_PTR(-EINVAL);
> +
> +			next_addr = sg_dma_address(s) + sg_dma_len(s);
> +		}
> +	}
> 
>  	/* Create a CMA GEM buffer. */
>  	cma_obj = __drm_gem_cma_create(dev, attach->dmabuf->size);
> diff --git a/include/drm/drm_gem_cma_helper.h
> b/include/drm/drm_gem_cma_helper.h index 58a739bf15f1f..214aa85adc8d5
> 100644
> --- a/include/drm/drm_gem_cma_helper.h
> +++ b/include/drm/drm_gem_cma_helper.h
> @@ -8,7 +8,9 @@
>   * struct drm_gem_cma_object - GEM object backed by CMA memory allocations
>   * @base: base GEM object
>   * @paddr: physical address of the backing memory
> - * @sgt: scatter/gather table for imported PRIME buffers
> + * @sgt: scatter/gather table for imported PRIME buffers. The table can
> have + *       more than one entry but they are guaranteed to have
> contiguous + *       DMA addresses.
>   * @vaddr: kernel virtual address of the backing memory
>   */
>  struct drm_gem_cma_object {

-- 
Regards,

Laurent Pinchart